Ophthalmological device

ABSTRACT

An ophthalmic instrument for the application of laser radiation in a patient&#39;s eye, particularly for the examination and/or surgical laser treatment of the cornea and the lens of the eye, includes a femtosecond laser, an objective and optical assemblies. The optical assemblies are arranged in front of the objective, and selectively vary the focus position in the coordinate direction X,Y and Z either within the region of the cornea or within the region of the lens of the eye. The objective or at least one lens group is movable relative to the eye. The variation of the position of the lens group objective shifts the focus position from the cornea to the lens of the eye and vice versa.

RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.14/006,017, filed Nov. 26, 2013 and entitled “Ophthalmological Device”,which is a National Phase entry of PCT Application No.PCT/EP2012/050035, filed Jan. 3, 2012, which claims priority to DEApplication No. 102011006085.5, filed Mar. 25, 2011, and U.S.Provisional Patent Application No. 61/467,712, filed Mar. 25, 2011,which applications are incorporated by reference herein in theirentirety.

FIELD OF THE INVENTION

The present invention relates to an ophthalmic instrument for the use oflaser radiation on and in the eye, especially for the examination and/orsurgical laser treatment of the cornea and the lens of the eye.

BACKGROUND

Ophthalmic instruments are used, for example, to correct an ametropia ofthe human eye by means of a surgical laser operation on the cornea. Amethod of particular importance is known as “LASIK” (laser in-situkeratomileusis), in which, by application of a pulsed laser beam,material is ablated from inside the cornea rather than from its surface.For this purpose, a flap is formed on the outer corneal surface, thethickness of this flap being substantially smaller than the thickness ofthe cornea. For the ablation treatment proper, the flap is folded back,whereupon a pulsed laser beam is used to ablate material from theexposed area to correct the ametropia. Thereafter, the flap is closedagain onto the treated surface.

To form the flap at a precisely defined depth of the cornea and asgently and precisely as possible, it has been suggested to usefemtosecond laser pulses, i.e. laser pulses having pulse widths smallerthan 10⁻¹²s. By application of such pulses it is possible to createlocalized optical ruptures in the cornea, known as photodisruptions, thesize of which is limited to a few micrometers. By positioning a densearray of many such disruptions in exactly defined places, the flap canbe made to measure very precisely. For the precise forming of the flapit is essential that the focus of the pulsed laser beam is exactlypositioned not only laterally but also, and mainly so, in the depth ofthe cornea, i.e. in the propagation direction of the laser beam.

In this connection, DE 10 2005 013 949 A1 describes a scanning devicefor, and a method of, focusing a beam of rays into a given volume. Thisscanning device is especially suitable for use in instruments intendedfor surgical laser treatment of the cornea with laser radiation pulsedin the femtosecond range. The device allows the laser light to befocused on any target points within the cornea.

DE 10 2008 027 358 A1 describes a laser system that can be used inophthalmic instruments for the analysis and treatment of the lens of theeye. Other than laser systems in comparable instruments, it has theadvantage that the detection of the laser light backscattered in thelens of the eye is possible with greater accuracy, so that a refractivesurgical therapy of the lens of the eye can be performed with higherprecision. For this therapy, laser radiation pulsed in the femtosecondrange is focused on selected target points within the lens of the eye.

The state of prior art described above regarding the medical examinationand surgical laser treatment of the cornea (situated at the periphery ofthe eye) on the one hand and the lens (situated within the eye) on theother has the disadvantage that the ophthalmic instruments availablesatisfy the requirements of one of these special applications only;i.e., they differ with regard to their imaging properties, inparticular: to their aperture, focal spot size, focus position in theeye, correction of the aperture aberration or correction of fieldaberrations to such an extent that they are exclusively suitable eitherfor the examination and treatment of the cornea or for the examinationand treatment of the lens of the eye.

This means that an oculist needs to procure two instruments, which isinefficient (a) with regard to acquisition cost and (b) because severalsingle-purpose instruments are seldom used to capacity. In addition,separate instruments involve extra time for getting adjusted at least tothe same eye of a patient being examined.

SUMMARY OF THE INVENTION

Departing from this, the invention is based on the problem of creatingan ophthalmic instrument that can be used for the examination andsurgical laser treatment of both the cornea and the lens of the eye.

According to the invention, this problem is solved by an ophthalmicinstrument of the kind described above, which comprises:

-   -   a femtosecond laser as a source of laser radiation,    -   an objective from which laser radiation emerges that is focused        in the direction of the patient's eye,    -   optical assemblies        -   which are arranged upstream of the objective, and        -   which are, in operative connection with the objective,            intended for varying the focus position in the coordinate            direction X,Y and Z, selectively either within the region of            the cornea or within the region of the lens of the eye,        -   with the objective itself being movable relative to the eye            or at least having one lens group whose position is movable            relative to the eye,        -   the variation of the objective or lens group position being            intended to shift the focus position from the region of the            cornea to the region of the lens of the eye and vice versa.

The distances are varied by shifting the respective lens groups of theobjective along their optical axis. Besides the focus position, thevariation of the distances also influences the correction of the imagingaberrations. Variation of the focus in depth causes changes, e.g., inspherical aberration, unless this is compensated by the lens movements.

Favorably, the lens groups of the objective can be displaced between twolimit positions that define two different specified distances along theoptical axis. One of these limit positions is assigned to the focuspositioned in the region of the cornea, the other to the focuspositioned in the region of the lens of the eye. In the sense of theinvention, positioning the focus “in the region of the cornea” meansthat the focus can be directed at any target points on or in the cornea,while positioning the focus “in the region of the lens of the eye” meansthat the focus can be directed at any target points on or in the lens ofthe eye. For the purpose of shifting from one limit position to theother, the movable lens groups are preferably coupled withelectromechanical drive units, which are connected to a control unit.

In principle, the shifting of lens groups of the objective correspondsto switching between two operating modes, with the instrument beingavailable for the examination and treatment of the lens of the eye inone operating mode, and for the examination and treatment of the corneain the other operating mode, which, in principle, solves the problem ofthe invention.

In an embodiment, an optical element of negative refractive power thatcan be moved in the direction of radiation is arranged upstream of theobjective, that movement being used to vary the focus position in thecoordinate direction Z, but only either within the region of the corneaor within the region of the lens of the eye. The moving of this elementvaries the divergence of the beam. Depending on the currently setdivergence angle, the objective focuses the beam on various positions inZ direction—either within the region of the cornea or within the regionof the lens of the eye.

The movable optical element may be configured, e.g., as a lens, areflective or a diffractive optical element. Preferably, it is a lens.To permit its controlled movement along the optical axis, the lens movesin a straight-line guide that is aligned in parallel with the beam path.

Also arranged upstream of the objective, there is a device fordeflecting the laser radiation in the X and Y coordinate directions,this lateral deflection also being possible only within either theregion of the cornea or the region of the lens of the eye.

In principle, the deflecting device may be designed in a manner that isknown per se. For example, it may merely consist of a mirror that istiltable about two different, preferably orthogonal, axes. Preferably,though, it comprises two mirrors arranged at a distance from each otherand oscillating relative to each other. This advantageous design permitsthe mirrors to be seated and adjusted and, thus, the focus to bepositioned laterally, with very high precision, though by simple means.

Between the two mirrors, an optical pupil element may be arranged thatimages the first mirror onto the second one, which results in a definedpupil position. In a precisely working optical system, a defined,permanent position of the pupil is a prerequisite for good correction.

Between the deflecting device and the objective, a beamsplitter may bearranged, by which part of the observation light coming from the corneaor the lens of the eye is coupled out for observation or imagingpurposes.

During the examination or treatment of the eye it is preferable to applyonto the cornea a contact glass with a concave contact surface in orderto suppress eye movement.

Moreover, the contact glass reduces the eye's refractive power and makesfocus correction easier.

In an example embodiment of the invention, a collecting lens is arrangeddownstream of the movable lens of negative refractive power, so thatboth elements together form a beam expander assembly, which expands thediameter of a parallel beam incident to the lens by a specified amount.Thus, if a parallel beam having a diameter d1 enters the beam expander,the emerging parallel beam will have an exit diameter d2>d1.

The exit diameter has an influence on the aperture angle on the side ofthe patient's eye. This given, it is within the scope of the inventionto provide structures for varying the aperture angle on the side of thepatient's eye, e.g., several exchangeable negative lenses of varieddivergence angles.

Exchanging the negative lenses for getting varied aperture angles on theside of the patient's eye can be done in connection with shifting thefocus position from the region of the cornea to the region of the lensof the eye and vice versa, or else according to the size of the eye tobe examined or treated, that size being defined preferably by the depthof the eye's anterior chamber. Such lens assemblies can be exchangedautomatically or manually.

The instrument according to the invention can be used to advantage forfast and easy adjustment of the focus position in three dimensionswithin the region required, i.e. that of the cornea or that of the lensof the eye. There is no need any more to change from one instrument toanother as in prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

Subject matter hereof may be more completely understood in considerationof the following detailed description of various embodiments inconnection with the accompanying figures. Below, the invention will beexplained in greater detail with reference to exemplary embodiments. Inthe accompanying drawings:

FIG. 1 is a schematic diagram of an ophthalmic instrument for theapplication of laser radiation according to prior art;

FIG. 2 depicts a variation of the arrangement shown in FIG. 1, featuringa beamsplitter for deflecting the observation beam towards a viewingtube with an eyepiece, or towards a camera,

FIG. 3 is a schematic diagram of the invented instrument for surgicallaser examination and treatment of the eye in a first preferredembodiment;

FIG. 4 depicts a variation of the embodiment shown in FIG. 3, featuringa beamsplitter for deflecting the observation beam towards a viewingtube with an eyepiece, or towards a camera;

FIG. 5 is a schematic diagram of the invented instrument for surgicallaser examination and treatment of the eye in a second preferredembodiment.

While various embodiments are amenable to various modifications andalternative forms, specifics thereof have been shown by way of examplein the drawings and will be described in detail. It should beunderstood, however, that the intention is not to limit the claimedinventions to the particular embodiments described. On the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the subject matter as defined bythe claims.

DETAILED DESCRIPTION

FIG. 1 shows an instrument for the treatment of a human eye 1 accordingto prior art. This instrument comprises a radiation source 2, whichemits a beam 3 of laser radiation pulsed in the femtosecond range, and ascanning device 4, with which the beam 3 can be focused on selectedpositions within the region of the cornea. On the cornea there is acontact glass 5 having a concave contact surface, which suppressesmovements of the eye 1 during examination or treatment.

The radiation source 2 is designed to emit, e.g., laser radiation in awavelength range around 1040 nm with a pulse width of about 200 fs.

On its end facing the beam 3 emerging from the radiation source 2, thescanning device 4 features an optical entrance system 6. Next to this inthe radiation direction, there is a deflecting device 7, which deflectsthe beam 3 emerging from the optical entrance system 6 laterally, i.e.in X and Y directions (across the Z direction of the incident beam 3)according to given control signals. Next to the deflecting device 7 inthe beam path there is an objective 8, which focuses the beam 3 in theregion of the cornea.

The deflecting device 7 is provided with two deflecting mirrors 9 and9′, which are mounted in bearings so as to be tiltable about axes notshown in FIG. 1. To simplify the diagram, the mirrors 9 and 9′ in FIG. 1are aligned in parallel; actually, however, the tilting axes areorthogonal to each other and to the optical axis of the optical entrancesystem 6, so that tilting the first mirror 9 deflects the beam 3 in Ydirection, and tilting the second mirror 9′ deflects it in the Xdirection orthogonal to the Y direction. The mirrors 9 and 9′ are drivenby actuators 10 and 10′, respectively, which are connected to a controldevice via signal paths (indicated by arrows). According to the desiredfocus position in lateral direction, the control device sends controlsignals to the actuators 10 and 10′, which then cause the mirrors 9 and9′ to tilt.

The optical entrance system 6 features a lens 11 of negative refractivepower that is movable relative to the deflecting device 7, and acollecting lens 12. The lens 11 is connected with a straight-line guide13, thanks to which it can be moved to vary the optically effectivedistance from the deflecting device 7. The movement of lens 11 inparallel to its optical axis can be effected, e.g., by means of a lineardrive 14, which is also connected with the control device (which is notshown). According to the desired focus position in Z direction, thecontrol device generates control signals sent to the linear drive 14.

The lens 11 and the collecting lens 12 are so designed that the opticalentrance system 6 acts as a beam expander, which expands the diameter ofthe beam 3. Thus, if a parallel beam 3 with a diameter d1 enters theoptical entrance system 6, a parallel beam 3 with a diameter d2>d1 willemerge from it.

The objective 8 is shown as a fixed lens 15; it focuses the beam 3emerging from the optical entrance system 6 on a position in the regionof the cornea, the position being defined by the lens 11 and thedeflecting device 7.

The position of the focus F in the depth of the region of the cornea isdefined by moving the 11 along its optical axis. The lateral position ofthe focus F is set by means of the deflecting device 7.

FIG. 2 shows a variation of the arrangement shown in FIG. 1, with abeamsplitter 16 arranged in the beam path between the deflecting device7 and the objective 8. By means of the beamsplitter 16, part of thelight coming from the cornea and shaped by the objective 8 into anobservation beam 17 is coupled out and deflected towards a viewing tube(not shown) with an eyepiece, or towards a camera (not shown either), sothat the cornea can be observed during examination or treatment.

Further details of this state of prior art can be found in DE 10 2005013 949 A1. Deviating from prior art, the problem of the invention issolved in such a way that the objective 8 consists of several lensgroups and is designed to allow itself or at least one lens group to bemoved relative to the eye, so that the distance variation effects ashifting of the focus position from the region of the cornea to theregion of the lens of the eye and vice versa.

FIG. 3 is a diagram of the invented instrument in a first preferredembodiment. Here, the objective 8 consists of two lens groups 15.1 and15.2, which are shown as single lenses for the sake of clarity. The lensgroup 15.2 is in a fixed position along the beam path, whereas the lensgroup 15.1 is arranged to as to be movable along the optical axis and,for this purpose, is coupled via with a straight-line guide with, e.g.,a linear drive 22, which, triggered by a control device (not shown),effects the movement.

The distance through which the lens group 15.1 is moved, whileprincipally depending on the control signal, is preferably defined bytwo limit positions. In FIG. 3, a first limit position is indicated bythe lens group 15.1 drawn in solid lines, whereas the second limitposition is drawn in broken lines.

This invariable moving distance defined by the limit positionscorresponds to the shifting of the focus position from the region of thecornea to the region of the lens of the eye and vice versa. As a result,the arrangement according to the invention can be used for theexamination and treatment of both the cornea and the lens of the eye. Aspatients' eyes naturally differ in size, one embodiment of the inventionprovides for the moving distance to be variable according to the eye 1.In this case there is only one fixed stop for cornea work, and acontinuously variable limit for eye lens work.

If the lens group 15.1 is in the first limit position, the focusposition can be varied in Z direction by means of lens 11 and in X and Ydirection by means of deflecting device 7 in such a way that this allowstargeting of all desired targets within the region of the lens of theeye but not beyond this region. Analogously this also applies to thesecond limit position and, thus, to the possibility of targeting alldesired targets within the region of the cornea.

The movement of lens group 15.1 between the two limit positions, or therelease of instructions for such movement, corresponds to the switchingof the invented instrument between two operating modes, with theinstrument being usable for the examination and treatment of the lens ofthe eye in one operating mode, and for the examination and treatment ofthe cornea in the other.

In an extended embodiment, an optional facility is provided to vary thebeam diameter 3′ in order to adapt the aperture angle a on the side ofthe eye 1 to the operating mode employed. If the ratio of the amounts ofthe refractive powers of lens 11 and the collecting lens 12 isdecreased, the diameter of the parallel beam 3′ emerging from thecollecting lens 12 will decrease, too, and, as a result, so will theaperture angle a on the side of the eye 1. A smaller aperture angle α isadvantageous for focus positioning on or in the lens of the eye, as infront (upstream) of the lens of the eye there is the pupil as arestricting aperture for the convergent beam 3 entering the lens of theeye, which improves the optical correction.

As shown in FIG. 3, a change of the ratio of the refractive powers inthe optical system 6, and, thus, of the diameter of the beam 3′ iseffected by exchanging several—here, for example, two—lenses 11 and 11′with differing refractive powers against one another. Either, one mayexchange merely lenses 11 and 11′ against one another, or the assemblyconsisting of radiation source 2, lens 11, lens holder 13 and lineardrive 14 against an assembly consisting of radiation source 2′, lens11′, lens holder 13′ and linear drive 14′.

Optionally, lens 11 and collecting lens 12 may be exchanged together asa pair to achieve the same effect.

The change of the divergence angle may, in a first version, bepositively coupled with switching between the operating modes, i.e., beeffected automatically, or, in alternative second version, as a functionof the size of the eye to be examined or treated. As a measure of theeye's size one may use, e.g., the depth of the eye's anterior chamber,which is separately ascertained prior to the start of an examination. Inthe first place, it is the movement of lens 15.1 that is derived fromthe measurement of the eye. The adaptation of the diameter of the beam3′ via the ratio of refractive indices within the optical system 6 maybe effected automatically in connection with switching between theoperating modes.

FIG. 4 shows a variation of the arrangement shown in FIG. 3, with abeamsplitter 16 arranged between the deflecting device 7 and theobjective 8. By application of the beamsplitter 16, part of the lightcoming from the eye and shaped by the objective 8 into an observationbeam 17 is coupled out and deflected towards a viewing tube (not shown)with an eyepiece, or towards a camera (not shown either), so that theeye detail being examined or treated can be observed.

FIG. 5 shows another preferred embodiment of the invention. In FIG. 5,components like those in the preceding examples have like referencenumbers.

Here, arranged between mirrors 9 and 9′ in the beam path is an opticalpupil system 18. It comprises two collecting lenses 19 and 19′, whichproject the beam 3 deflected by mirror 9 onto mirror 9′, with anintermediate real image being produced in the air between the collectinglenses 19 and 19′. In this way, a fixed position of the pupil results,which makes an optically favorable design of the objective 8 possible.Moreover, due to each of the mirrors 9 and 9′ being imaged in the other,mirror 9′ can be kept small. The mirrors 9 and 9′ may be, e.g., ofelliptical shape.

In this embodiment of the invention, the objective 8 is a multipleassembly, comprising an entrance group of lenses 20, a tube lens 21, andthe lens groups 15.1 and 15.2.

The beam 3 laterally deflected by the deflecting device 7 enters theentrance group of lenses 20, which focuses it to form an intermediatereal image. The tube lens 21 projects the intermediate image toinfinity. A beamsplitter 16 deflects the beam 3 to the lens groups 15.1and 15.2.

Changing the focus position in the coordinate directions X, Y and Z iseffected as described in the preceding embodiment example. The sameapplies to the switching between the two operating modes by moving thelens group 15.1 between two limit positions, with the instrument beingconfigured for the examination and treatment of the lens of the eye inone mode, and for the examination and treatment of the cornea in theother.

Advantageously, all optical components are designed in such a way thatthe intermediate real images are situated in air, so that high-intensitylaser radiation cannot cause any optical breakdown in opticalcomponents.

In all embodiments of the invention, the radiation source 2, the opticalentrance system 6 and the objective 8 are designed for the beam 3 tohave a diameter of less than 5 micrometers at the focus. Preferably, theobjective 8 has an aperture greater than 0.35.

Various embodiments of systems, devices, and methods have been describedherein. These embodiments are given only by way of example and are notintended to limit the scope of the claimed inventions. It should beappreciated, moreover, that the various features of the embodiments thathave been described may be combined in various ways to produce numerousadditional embodiments. Moreover, while various materials, dimensions,shapes, configurations and locations, etc. have been described for usewith disclosed embodiments, others besides those disclosed may beutilized without exceeding the scope of the claimed inventions.

Persons of ordinary skill in the relevant arts will recognize that thesubject matter hereof may comprise fewer features than illustrated inany individual embodiment described above. The embodiments describedherein are not meant to be an exhaustive presentation of the ways inwhich the various features of the subject matter hereof may be combined.Accordingly, the embodiments are not mutually exclusive combinations offeatures; rather, the various embodiments can comprise a combination ofdifferent individual features selected from different individualembodiments, as understood by persons of ordinary skill in the art.Moreover, elements described with respect to one embodiment can beimplemented in other embodiments even when not described in suchembodiments unless otherwise noted.

Although a dependent claim may refer in the claims to a specificcombination with one or more other claims, other embodiments can alsoinclude a combination of the dependent claim with the subject matter ofeach other dependent claim or a combination of one or more features withother dependent or independent claims. Such combinations are proposedherein unless it is stated that a specific combination is not intended.

Any incorporation by reference of documents above is limited such thatno subject matter is incorporated that is contrary to the explicitdisclosure herein. Any incorporation by reference of documents above isfurther limited such that no claims included in the documents areincorporated by reference herein. Any incorporation by reference ofdocuments above is yet further limited such that any definitionsprovided in the documents are not incorporated by reference hereinunless expressly included herein.

For purposes of interpreting the claims, it is expressly intended thatthe provisions of 35 U.S.C. §112(f) are not to be invoked unless thespecific terms “means for” or “step for” are recited in a claim.

LIST OF REFERENCE NUMBERS

-   -   1 eye    -   2 radiation source    -   3 beam    -   4 scanning device    -   5 contact glass    -   6 optical entrance system    -   7 deflecting device    -   8 objective    -   9, 9′ mirrors    -   10, 10′ actuators    -   11 first lens    -   12 collecting lens    -   13 lens holder    -   14 linear drive    -   15.1, 15.2 lens groups    -   16 beamsplitter    -   17 observation beam    -   18 optical pupil system    -   19,19′ collecting lenses    -   20 entrance group of lenses    -   21 tube lens    -   linear drive

The invention claimed is:
 1. An ophthalmic instrument for theapplication of laser radiation in an eye, including for examinationand/or surgical laser treatment of a cornea and a lens of the eye, theophthalmic instrument comprising: a femtosecond laser as a radiationsource for laser radiation; an optical entrance system; an objectivefrom which a beam emerges that is focused in a direction of the eye;optical assemblies which are arranged in front of the objective as seenin a beam direction and which, in operative connection with theobjective, selectively vary a focus position in a coordinate directionX,Y and Z either within a region of the cornea or within a region of thelens of the eye; an aperture angle α on a side of the objective facingthe eye being variable by variation of a refractive power ratio withinthe optical entrance system and, thus, variation of a diameter of a beamemerging from the optical entrance system is also variable, the apertureangle α being smaller when the focus is positioned in a region of thelens than when the focus is positioned in a region of the cornea.
 2. Theophthalmic instrument as claimed in claim 1, further comprising: infront of the objective, a lens of negative refractive power that is partof the optical entrance system and that is movable along the beamdirection, the movement of which varies the focus position in thecoordinate direction Z; and a deflecting device located in front of theobjective that varies the focus position in the coordinate directions Xand Y, wherein the deflecting device is located between the lens and theobjective.
 3. The ophthalmic instrument as claimed claim 2, in which theoptical entrance system further comprises a collecting lens arrangedbehind the lens of negative refractive power as seen in the beamdirection.
 4. The ophthalmic instrument as claimed claim 3, in which thelens of negative refractive power is operably coupled with a lineardrive.
 5. The ophthalmic instrument as claimed in claim 3, in which apair of the lens of negative refractive power and the collecting lens isone among several pairs which are exchangeable with one another toeffect the variation of the refractive power ratio within the opticalentrance system.
 6. The ophthalmic instrument as claimed in claim 2, inwhich the lens of negative refractive power is one among several lenseswhich are exchangeable against one another to effect the variation ofthe refractive power ratio within the optical entrance system.
 7. Theophthalmic instrument as claimed in claim 2, in which an assemblycomprising the radiation source and the negative-power lens isexchangeable with assemblies comprising lenses with different negativepowers.
 8. The ophthalmic instrument as claimed in claim 2, in which thedeflecting device comprises two mirrors that are arranged at a distancefrom each other and that can be tilted relative to each other.
 9. Theophthalmic instrument as claimed in claim 8, further comprising anoptical pupil system comprising two collecting lenses arranged betweenthe mirrors.
 10. The ophthalmic instrument as claimed in claim 2,further comprising a beamsplitter arranged in a beam path between adeflecting device and the objective that couples out a partial beamdirected at an eyepiece or a camera.
 11. The ophthalmic instrument asclaimed in claim 1, in which the variation of the aperture angle α onthe side of the objective facing the eye is coupled with shifting of afocus position from the region of the cornea to the region of the lensof the eye and vice versa.
 12. The ophthalmic instrument as claimed inclaim 11, in which an amount of focus shifting between the cornea andthe lens of the eye is a function of an individual depth of an anteriorchamber.